An improvement of laser-focused peak intensity has been achieved in a JAERI 100 TW Ti:sapphire chirped-pulse amplifier chain with a feedback controlled adaptive optics system operating at a 10 Hz repetition rate. The Strehl ratio was enhanced to 0.8 by means of a Bimorph deformable mirror with a Shack-Hartmann wave-front sensor. Measurements of optical parameters of the laser pulse and an experimental tunneling ionization yield of helium have practically confirmed focusing to ultrarelativistic intensities of over 1020W∕cm2 within 16% accuracy.

In both scientific and industrial laser beam applications is essential for users to know what could be expected from the laser beam. That is why analysis of the laser beam parameters is very important during laser use in various industrial and scientific applications. To describe the beam one can use a beam quality factor M 2 that characterizes the degree of imperfection of a laser beam. There are many methods of beam quality determination. The most common way is to use a device based on techniques described in the International Standard ISO11146 "Test methods for laser beam parameters: Beam widths, divergence angle and beam propagation factor". For example we can use M2-sensor that we design and produce in our Lab. The measurement of the beam quality factor according to ISO11146 is not a simple procedure and might take a long time. And for some applications fast beam quality determination is needed. Moreover sometimes it is not necessary to know the exact value of M 2 , only estimation of M 2 is just needed. And for the beam quality estimation we suggest to use Shack-Hartmann wavefront sensor. With this sensor we can easily and fast measure the wavefront of the beam and then according to the wavefront calculate M 2 . The comparison of two sensors is presented. Advantages and disadvantages are pointed out.

The bimorph deformable mirror with a diameter of 320 mm, including 127 control electrodes, has been developed and tested. The flatness of the initial mirror surface of about 1 μm (P-V) was achieved by mechanically adjusting the mirror substrate fixed in the metal mount. To correct for the aberrations and improve the beam focusing in the petawatt Ti:Sa laser, the wide-aperture adaptive optical system with the deformable mirror and Shack–Hartmann wavefront sensor was developed. Correction of the wavefront aberrations in the 4.2 PW Ti:Sa laser using the adaptive system provided increases the intensity in the focusing plane to a value of 1.1 × 1023 W/cm2

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